For the purpose of successively transmitting large sized data on an IP network, one IP node fragments data into successive IP packets and transmits the successive IP packets to another node.
The length of a packet that can be transmitted between a source node and a destination node at one time is called a Maximum Transfer Unit (MTU). In the above method, when IP packets, each including a payload, transmitted and received between nodes are larger than the MTU, each payload is fragmented into several pieces. An IP layer fragments the packets according to an MTU of a physical network in a transmission section.
In a conventional technique, a packet relay node, such as a router, located between a transmitting node (i.e., a source node) and a receiving node (i.e., a destination node) does not reassemble fragmented IP packets, which will be reassembled by an IP layer of the destination node.
In view of efficiency of message management, some layers, such as a TCP layer, usually fragment packets using an entire size of an MTU and transmit fragmented packets to the IP layer. However, on a layer such as a User Datagram Protocol (UDP), IP may fragment a payload having a maximum of 65,536 bytes size provided by an upper application layer in consideration of the MTU in order to transfer the payload to the IP layer, if necessary.
A difference in fragmentation between IPv4 and IPv6 is that only an IPv6 source node is allowed to perform fragmentation with a Fragment Header (FH) that is an IPv6 extension header being added and used for identifying fragmented packets while routers on a packet transmission path are not allowed to perform the fragmentation.
FIG. 1 illustrates an example in which a payload of each of several types of packets, such as Real-Time Transport Protocol (RTP)/User Datagram Protocol (UDP)/Internet Protocol (IP), UDP/IP and TCP/IP packets, having a greater size than an MTU, is fragmented, and the resultant fragmented packets are assembled back into an original packet. Referring to FIG. 1, only a first fragmented packet including a header, such as an RTP/UDP/IP, UDP/IP or TCP/IP packet, satisfies a header compression profile of a Packet Data Convergence Protocol (PDCP) entity, and other fragmented packets all have a type of IP packets merely carrying a payload of an upper layer.
This means that only the first fragmented packet satisfies the header compression profile previously set in the PDCP entity and other fragmented packets are transmitted without satisfying the header compression profile set in the PDCP entity. In this case, the FH is located between the IP header of each fragmented packet and the payload of an original packet.
Accordingly, when the fragmented IP packets are received by the PDCP entity via a PDCP Service Access Point (SAP), radio resources are wasted due to duplicate transmission of IP headers having the same fragmentation information. Since the fragmented packets are transmitted without satisfying the header compression profile set in the PDCP entity, a header compression algorithm does not correctly operate and compression is not performed due to the presence of fragmented packets having a different profile from the header compression profile, leading to incorrect information exchange between header compression protocols and additional radio resource waste. The radio resource waste becomes severe for an IPv6 packet having a larger header.
Furthermore, when one piece of an IP packet having a fragmented payload among IP packets transmitted to user equipment is lost, all the IP packets must be retransmitted from the network. This causes heavy overhead on communication.
Thus, there is a need for an efficient method for resolving problems of low efficiency of header compression protocol, waste of radio resources, and packet transmission overhead.